In the prior art, sprayed coatings having corrosion resistance are used for protecting substrates in a variety of service environments. While aluminum, chromium and similar metal oxides are often used as the thermal spray material, these spray materials are inadequate for use in the semiconductor fabrication process which may include exposure to hot plasma, corrosive attacks, and in particular, treatment in a halogen-based corrosive gas plasma atmosphere.
The halogen-based corrosive gas plasma atmosphere used in the fabrication of semiconductor devices contains fluorine gases such as SF6, CF4, CHF3, ClF3 and HF and chlorine gases such as Cl2, BCl3 and HCl.
Known articles which can be used in such extremely corrosive atmospheres include, for example, articles having corrosion resistant coatings obtained by spraying yttrium oxide (Patent Document 1) and yttrium fluoride (Patent Document 2) to their surface. While rare earth oxide sprayed articles are generally prepared by plasma spraying rare earth oxide, they are long used as the sprayed articles in the industrial semiconductor fabrication process because of least technical problems. On the other hand, the rare earth fluoride sprayed coatings suffer from a technical problem despite good corrosion resistance. The plasma spraying of rare earth fluoride has the problem that when the rare earth fluoride is passed through a flame at 3,000° C. or higher for melting, the fluoride can be decomposed so that the material partially converts to a mixture of rare earth fluoride and rare earth oxide. For this reason, practical utilization of rare earth fluoride sprayed articles is delayed as compared with the rare earth oxide sprayed articles.